#include <stdio.h>

bool FindChar(char* pInputString, char* pChar)
{
	int arr[256];
	for(int i = 0 ; i < 256 ; ++i)
		arr[i] = 0;
	char *p = pInputString;
	int idx = 1;
	while(*p)
	{
		//printf("p : %c, idx : %d \n",*p,idx);
		if(arr[*p] == 0)
			arr[*p] = idx;
		else if(arr[*p] > 0)
			arr[*p] = -1;
		++idx;
		++p;
	}
	//printf("test\n");
	int min = 0x7fffffff;
	idx = -1;
	for(int i = 0 ; i < 256 ; ++i)
	{
		if(arr[i] > 0 && min > arr[i])
		{
			//printf("min : %d\n",min);
			min = arr[i];
			idx = i;
		}
	}
	if(idx == -1)
	{
		*pChar = '.';
		return false;
	}
	*pChar = idx;
	return true;
}


int main()
{

	char s[1024],c;
	while(scanf("%s",s) != EOF)
	{
		FindChar(s,&c);
		printf("%c\n",c);
	}
	return 0;
}